Recently, mobile communication systems have developed remarkably, but for high capacity data communication services, the performance of mobile communication systems cannot match that of existing wired communication systems. Accordingly, technical developments for IMT-2000, which is a communication system allowing high capacity data communications, are being made and standardization of such technology is being actively pursued among various companies and organizations.
A universal mobile telecommunication system (UMTS) is a third generation mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM). The UMTS aims to provide improved mobile communication service based on a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the United States, and TTA of Korea formed a Third Generation Partnership Project (3GPP) for creating the detailed specifications of the UMTS technology.
Within the 3GPP, in order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created for performing the standardization of the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the standard specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 illustrates an exemplary basic structure of a general UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a mobile terminal (or user equipment: UE) 10, a UTRAN 100, and a core network (CN) 200.
The UTRAN 100 includes one or more radio network sub-systems (RNS) 110, 120. Each RNS 110, 120 includes a radio network controller (RNC) 111, and a plurality of base stations or Node-Bs 112, 113 managed by the RNC 111. The RNC 111 handles the assigning and managing of radio resources, and operates as an access point with respect to the core network 200.
The Node-Bs 112, 113 receive information sent by the physical layer of the terminal through an uplink, and transmit data to the terminal through a downlink. The Node-Bs 112, 113, thus, operate as access points of the UTRAN 100 for the terminal.
A primary function of the UTRAN 100 is forming and maintaining a radio access bearer (RAB) to allow communication between the terminal and the core network 200. The core network 200 applies end-to-end quality of service (QoS) requirements to the RAB, and the RAB supports the QoS requirements set by the core network 200. As the UTRAN 100 forms and maintains the RAB, the QoS requirements of end-to-end are satisfied. The RAB service can be further divided into an Iu bearer service and a radio bearer service. The Iu bearer service supports a reliable transmission of user data between boundary nodes of the UTRAN 100 and the core network 200.
The core network 200 includes a mobile switching center (MSC) 210 and a gateway mobile switching center (GMSC) 220 connected together for supporting a circuit switched (CS) service, and a serving GPRS support node (SGSN) 230 and a gateway GPRS support node 240 connected together for supporting a packet switched (PS) service.
The services provided to a specific terminal are roughly divided into the circuit switched (CS) services and the packet switched (PS) services. For example, a general voice conversation service is a circuit switched service, while a Web browsing service via an Internet connection is classified as a packet switched (PS) service.
For supporting circuit switched services, the RNCs 111 are connected to the MSC 210 of the core network 200, and the MSC 210 is connected to the GMSC 220 that manages the connection with other networks.
For supporting packet switched services, the RNCs 111 are connected to the SGSN 230 and the GGSN 240 of the core network 200. The SGSN 230 supports the packet communications going toward the RNCs 111, and the GGSN 240 manages the connection with other packet switched networks, such as the Internet.
Various types of interfaces exist between network components to allow the network components to transmit and receive information to and from each other for mutual communication therebetween. An interface between the RNC 111 and the core network 200 is defined as an Iu interface. In particular, the Iu interface between the RNCs 111 and the core network 200 for packet switched systems is defined as “Iu-PS,” and the Iu interface between the RNCs 111 and the core network 200 for circuit switched systems is defined as “Iu-CS.”
FIG. 2 illustrates a structure of a radio interface protocol between the terminal and the UTRAN according to the 3GPP radio access network standards.
As shown in FIG. 2, the radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane (U-plane) for transmitting user data and a control plane (C-plane) for transmitting control information.
The user plane is a region that handles traffic information of the user, such as voice or Internet protocol (IP) packets, while the control plane is a region that handles control information for an interface of a network, maintenance and management of a call, and the like.
The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model. Each layer will be described in more detail as follows.
The first layer (L1), namely, the physical layer, provides an information transfer service to an upper layer by using various radio transmission techniques. The physical layer is connected to an upper layer called a medium access control (MAC) layer, via a transport channel. The MAC layer and the physical layer send and receive data with one another via the transport channel.
The second layer (L2) includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer.
The MAC layer provides an allocation service of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to an upper layer called the radio link control (RLC) layer, via a logical channel.
Various logical channels are provided according to the kind of transmitted information. In general, when information of the control plane is transmitted, a control channel is used. When information of the user plane is transmitted, a traffic channel is used. A logical channel may be a common channel or a dedicated channel depending on whether the logical channel is shared. Logical channels include a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a common traffic channel (CTCH), a common control channel (CCCH), a broadcast control channel (BCCH) and a paging control channel (PCCH) or a Shared Channel Control Channel (SHCCH). The BCCH provides information including information utilized by a terminal to access a system. The PCCH is used by the UTRAN to access a terminal.
A Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) refers to a method of providing streaming or background services to a plurality of UEs using a downlink-dedicated MBMS radio bearer that utilizes at least one of point-to-multipoint and point-to-point radio bearer. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals through the MBMS radio bearer only while the session is ongoing.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs within a broadcast area, for example the domain where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE group within a multicast area, for example the domain where the multicast service is available.
For purposes of MBMS, additional traffic and control channels exist. For example, an MCCH (MBMS point-to-multipoint Control Channel) is used for transmitting MBMS control information while an MTCH (MBMS point-to-multipoint Traffic Channel) is used for transmitting MBMS service data.
The different logical channels that exist are listed below:

The MAC layer is connected to the physical layer by transport channels and can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, and a MAC-hs sub-layer according to the type of transport channel to be managed.
The MAC-b sub-layer manages a BCH (Broadcast Channel), which is a transport channel handling the broadcasting of system information. The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal. Accordingly, the MAC-d sub-layer of the UTRAN is located in a serving radio network controller (SRNC) that manages a corresponding terminal, and one MAC-d sub-layer also exists within each terminal (UE).
The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH) or a downlink shared channel (DSCH), which is shared by a plurality of terminals, or in the uplink the Radio Access Channel (RACH). In the UTRAN, the MAC-c/sh sub-layer is located in a controlling radio network controller (CRNC). As the MAC-c/sh sub-layer manages the channel being shared by all terminals within a cell region, a single MAC-c/sh sub-layer exists for each cell region. Also, one MAC-c/sh sublayer exists in each terminal (UE). Referring to FIG. 3, possible mapping between the logical channels and the transport channels from a UE perspective is shown. Referring to FIG. 4, possible mapping between the logical channels and the transport channels from a UTRAN perspective is shown.
The RLC layer supports reliable data transmissions, and performs a segmentation and concatenation function on a plurality of RLC service data units (RLC SDUs) delivered from an upper layer. When the RLC layer receives the RLC SDUs from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner upon considering processing capacity, and then creates certain data units with header information added thereto. The created data units are called protocol data units (PDUs), which are then transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
The BMC layer schedules a cell broadcast message (referred to as a ‘CB message’, hereinafter) received from the core network, and broadcasts the CB messages to terminals located in a specific cell(s). The BMC layer of the UTRAN generates a broadcast/multicast control (BMC) message by adding information, such as a message ID (identification), a serial number, and a coding scheme to the CB message received from the upper layer, and transfers the BMC message to the RLC layer. The BMC messages are transferred from the RLC layer to the MAC layer through a logical channel, i.e., the CTCH (Common Traffic Channel). The CTCH is mapped to a transport channel, i.e., a FACH, which is mapped to a physical channel, i.e., a S-CCPCH (Secondary Common Control Physical Channel).
The PDCP (Packet Data Convergence Protocol) layer, as a higher layer of the RLC layer, allows the data transmitted through a network protocol, such as an IPv4 or IPv6, to be effectively transmitted on a radio interface with a relatively small bandwidth. To achieve this, the PDCP layer reduces unnecessary control information used in a wired network, a function called header compression.
A radio resource control (RRC) layer is located at a lowermost portion of the L3 layer. The RRC layer is defined only in the control plane, and handles the control of logical channels, transport channels, and physical channels with respect to setup, reconfiguration, and release or cancellation of radio bearers (RBs). The radio bearer service refers to a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. In general, the setup of the radio bearer refers to the process of defining the characteristics of a protocol layer and a channel required for providing a specific data service, as well as respectively setting detailed parameters and operation methods.
The RLC layer can belong to the user plane or to the control plane depending upon the type of layer connected at the upper layer of the RLC layer. That is, if the RLC layer receives data from the RRC layer, the RLC layer belongs to the control plane. Otherwise, the RLC layer belongs to the user plane.
The different possibilities that exist for the mapping between the radio bearers and the transport channels are not always possible. The UE/UTRAN deduces the possible mapping depending on the UE state and the procedure that the UE/UTRAN is executing. The different states and modes are explained in more detail below.
The different transport channels are mapped onto different physical channels. For example, the RACH transport channel is mapped on a given PRACH, the DCH can be mapped on the DPCH, the FACH and the PCH can be mapped on the S-CCPCH, the DSCH is mapped on the PDSCH and so on. The configuration of the physical channels is given by an RRC signaling exchange between the RNC and the UE.
The RRC mode refers to whether there exists a logical connection between the RRC of the terminal and the RRC of the UTRAN. If there is a connection, the terminal is said to be in RRC connected mode. If there is no connection, the terminal is said to be in idle mode. Because an RRC connection exists for terminals in RRC connected mode, the UTRAN can determine the existence of a particular terminal within the unit of cells, for example which cell or set of cells the RRC connected mode terminal is in, and which physical channel the UE is listening to. Thus, the terminal can be effectively controlled.
In contrast, the UTRAN cannot determine the existence of a terminal in idle mode. The existence of idle mode terminals can only be determined by the core network. Specifically, the core network can only detect the existence of idle mode terminals within a region that is larger than a cell, such as a location or a routing area. Therefore, the existence of idle mode terminals is determined within large regions. In order to receive mobile communication services such as voice or data, the idle mode terminal must move or change into the RRC connected mode. The possible transitions between modes and states are shown in FIG. 5.
A UE in RRC connected mode can be in different states, such as a CELL_FACH state, a CELL_PCH state, a CELL_DCH state or a URA_PCH state. Depending on the states, the UE listens to different channels. For example a UE in CELL_DCH state will try to listen (amongst others) to DCH type of transport channels, which comprises DTCH and DCCH transport channels, and which can be mapped to a certain DPCH. The UE in CELL_FACH state will listen to several FACH transport channels which are mapped to a certain S-CCPCH physical channel. The UE in PCH state will listen to the PICH channel and to the PCH channel, which is mapped to a certain S-CCPCH physical channel.
The UE also carries out different actions depending on the state. For example, based on different conditions, a UE in CELL_FACH will start a CELL Update procedure each time the UE changes from the coverage of one cell into the coverage of another cell. The UE starts the CELL Update procedure by sending to the NodeB a Cell Update message to indicate that the UE has changed its location. The UE will then start listening to the FACH. This procedure is additionally used when the UE comes from any other state to CELL_FACH state and the UE has no C-RNTI available, such as when the UE comes from the CELL_PCH state or CELL_DCH state, or when the UE in CELL_FACH state was out of coverage.
In the CELL_DCH state, the UE is granted dedicated radio resources, and may additionally use shared radio resources. This allows the UE to have a high data rate and efficient data exchange. However, the radio resources are limited. It is the responsibility of the UTRAN to allocate the radio resources amongst the UEs such that they are efficiently used and ensure that the different UEs obtain the quality of service required.
A UE in CELL_FACH state has no dedicated radio resources attributed, and can only communicate with the UTRAN via shared channels. Thus, the UE consumes few radio resources. However, the data rate available is very limited. Also, the UE needs to permanently monitor the shared channels. Thus, UE battery consumption is increased in the case where the UE is not transmitting.
A UE in CELL_PCH/URA_PCH state only monitors the paging channel at dedicated occasions, and therefore minimizes the battery consumption. However, if the network wishes to access the UE, it must first indicate this desire on the paging occasion. The network may then access the UE, but only if the UE has replied to the paging. Furthermore, the UE can only access the network after performing a Cell Update procedure which introduces additional delays when the UE wants to send data to the UTRAN.
Currently, via the Internet, two terminals (e. g. two PCs) can communicate voice, video and data not only via a strict a wireline network, but also through a telecommunication system wherein at least part of the communication path is wireless. Such a telecommunication system includes a radio access network (RAN), such as the RAN providing access to the UMTS (Universal Mobile Telecommunications System) being developed under the auspices of 3GPP (Third Generation Partnership Program). To enable such multimedia (MM) communication between two terminals, the UMTS includes a component referred to as IMS (Internet Protocol Multimedia Subsystem).
The 3GPP system (UMTS) in its first release (R99) was designed to be backward compatible with the existing GSM (Global System for Mobile Communications) circuit switched infrastructure. Because the costs to procure and maintain the very proprietary hardware of circuit switched systems are very high and because much of the bandwidth used to transmit user data is lost, the 3GPP system is slowly evolving toward an all-IP core network. Thus, the existing circuit switched infrastructure will ultimately be outdated and replaced by IP-based hardware, which is open, scalable, and cheaper to procure and maintain due to a more competitive market. Therefore, through REL-4 and REL-5 of the 3GPP specifications, more and more importance is given to IP-based architecture. The IMS is introduced first to handle classical circuit switched services, such as voice over IP (VoIP), and second to handle all multimedia services provided to subscribers.
Referring to FIG. 6, the IMS (IP Multimedia Subsystem) is an extension of the PS (packet-switched) Core Network (CN) of UMTS. It uses a Session Initiation Protocol (SIP) to set up, maintain and terminate voice and multimedia sessions.
An example of a session is a series of communications in which a user is first engaged in a voice communication, and then receives an incoming IP video communication but decides not to accept the IP video communication. Instead, the user diverts the incoming video to a messaging system, which then posts in the user's mail box a message indicating that the user has new mail, i.e. the video message.
SIP is a part of the overall Internet Engineering Task Force (IETF) multimedia data and control architecture. It is used in conjunction with other IETF protocols, such as a Session Description Protocol (SDP) and a Real-Time Protocol (RTP). SIP is a signaling protocol for handling the setup, modification, and teardown of MM sessions, and in combination with the protocols with which it is used, describes the session characteristics of a communication session to potential session participants. Usually, RTP is used to exchange the media (audio, voice or data) during the communication session, but SIP allows any transport protocol to be used.
Also, SIP messages (signaling) usually pass through some of the same equipment as the media to be exchanged during a communication session. However, it is important to maintain a logical separation between SIP signaling and the communication of the media (the session data) because the SIP signaling for a communication session might pass through one or more proxy servers while the media stream uses a more direct path between the participants in the communication session.
Still referring to FIG. 6, because of the services provided by the IMS included in the CN PS domain, and as already indicated above, a personal computer/terminal equipment (PC/TE) coupled to the UMTS via a MT (mobile terminal) can communicate voice, video and data to another PC connected to the Internet. Preferably, the communication may be made to any entity supporting IMS, such as another mobile terminal. The PC/TE may communicate with the MT in any number of ways, such as using Bluetooth (BT) technology, for example. In such a communication, the PC/TE and the MT, so coupled in combination, make up what is called the user equipment (UE). In general, a UE device is an MT coupled to a terminal equipment (TE) device, such as but not necessarily restricted to, a PC. The UE device may be an IMS-enabled mobile phone, including a MT coupled to a TE device such as a specialized processor, wherein the specialized processor is not what is generally referred to as a PC. It should be realized that the above logical entities can be combined in a single physical device.
The RTP protocol comprises data part RTP packets and control part packets, such as RTCP (RTP Control Protocol) packets. The RTP packets contain media data. The RTCP packets contain control information, such as information for synchronizing the RTP media streams, user address information, and information on available data rate, etc.
In general, RTP and RTCP have different characteristics in terms of bandwidth requirement, packet size and delay requirements. Typically, for a VoIP service, the RTP packets comprise short packets (e.g. several tens of octets) that are sent regularly (e.g. every 20 msec), but need to be delivered quickly. The RTCP packets are sent rarely (e.g. every 5 sec) and can tolerate higher delays, but have a much bigger size (e.g. several hundreds of octets).
The RTP protocol is a protocol that normally uses an IP (Internet Protocol) and a UDP (User Datagram Protocol) as a transport protocol. Referring to FIG. 7, a UDP packet is used to transport the RTP/RTCP packets, wherein a UDP header provides a port number. Each media stream uses one UDP port number for RTP and one UDP port number for RTCP. However, the port number cannot be used to know whether the UDP packet contains an RTP or RTCP packet because any port number can be assigned to the stream carrying the RTP or RTCP packet. Moreover, the information is currently not provided to the RNC or AS (Access Stratum) of the UE.
The IP header is used to route the packet through the Internet from the source address to the destination address. The IP header also allows segmentation. The IP header contains information regarding the type of the included packet, i.e. whether a UDP packet or a different type of packet is included.
Therefore, what is needed is a method for distinguishing between RTP packets and RTCP packets included in the UDP packet.